# copied from KineticsKit to remove visual May 2003 jch
import math
from Point import Point

# m = mass
# v = velocity
# F = force
# fixed is whether the Physics system will move it.
# pos[ition]

class Mass:
    """Physical model and visual representation of a mass.
    """

    #rho = 8900 # Cu
    rho = 23.8732414637845 # for backwards compatibility
    factor = 3. / (4 * math.pi * rho)

    def __init__(self, m, pos, fixed=0, v=[0,0,0]):
        """Construct a mass.
        """
        self.m = float(m)
        self.pos = Point(pos)
        self.fixed = fixed
        self.v = Point(v)
        self.F = Point([0., 0., 0.])

    def calcGravityForce(self, g):
        """Calculate the gravity force.
        """
        # gforce = m * g
        self.F -= Point([0, self.m * g, 0])

    def calcViscosityForce(self, viscosity):
        """Calculate the viscosity force.
        """
        # Fviscosity = - v * viscosityFactor
        self.F -= self.v * viscosity

    def calcNewLocation(self, dt):
        """Calculate the new location of the mass.
        """
        # F = m * a = m * dv / dt  =>  dv = F * dt / m
        dv = self.F * dt / self.m
        self.v += dv
        # v = dx / dt  =>  dx = v * dt
        self.pos += self.v * dt

    def clearForce(self):
        """Clear the Force.
        """
        self.F = Point([0., 0., 0.])

    def getPosition(self):
        return self.pos

    def setPosition(self,point):
        return self.pos.Assign(point)